Hi Bob,
I can speak a bit of Romany and there's more Gypsy blood in my guitar than me. Traveller 'cant' is too vague to be a term I understand. Do you mean Irish Shelta, or a mixture of English and Romany words?
My best friend is a Romany, and will not mix English with Romany ever.
He likes teasing me by speaking it so fast that I miss his meaning.
Please don't take offence Bob if I respectfully point out that the Late Charlie Smith of the Gypsy council,(of which my wife was the chairman for a year or so} was at pains to ask all concerned to spell Gypsy or Traveller with a capital letter as a mark of respect, in the same way as English or French as you rightly point out. This is in no way meant to be an overly critical or aggressive post to you or anybody else.
kind regards